A number of processes for manufacturing multi-coloured detergent bars have been commercially used and are well characterised in literature.
In one process streams of detergent noodles of differing visual appearance are mixed prior to the final plodder stage and the mixed mass is extruded, cut and stamped to form bars. The product has a multi-coloured appearance throughout consisting of striations parallel to the axis of extrusion. At the stamping stage the bar may be stamped perpendicular to the axis of extrusion, as is normal in soap processing, or the bar may be stamped at an angle to the axis or the cut billet may be stamped end on i.e., along the axis of extrusion.
The final stages of detergent bar manufacture will normally comprise a refiner stage leading into a plodder stage connected, preferably, by a vacuum chamber. The detergent feedstock is subjected to shearing and mixing action while progressing through the refiner plodder and noodles of detergent are formed by forcing the detergent mass through a multi-apertured plate against which, preferably, a rotating knife cuts the extrudate into consistent sized noodles. The present invention is specific to the processing arrangement in which a refiner stage precedes the plodder stage.